This invention pertains to methods and apparatus for constructing vertically, oriented, or near-vertical, concrete structures. “Near-vertical” means that the structure, or segments of whole structures, can be purposely constructed at a slope (or “out-of-plumb”, which is not to be confused with construction plumbness tolerances), tapered (so that an inside or outside surface is not plumb), curved in vertical section (for example, as in a cooling tower structure), or a combination of these geometries. Example of such vertical or near-vertical structures include, without limitation, closed-form shell structures such as silos, stacking tubes, towers, cooling towers, chimneys, hollow columns, tanks, tank stems, bins, ponds, shear wall chambers, and retaining wall enclosures. Such structures can also be open-form structures, such as retaining walls, sound walls, shear walls, bearing walls, bunkers, curtain walls, columns, and column bents. Such structures further include a combination of closed-form and open-form structures, known as combination-form structures. Closed-form structures are those structures where the walls of the structure in a plan view can be traced an infinite distance (i.e., without reaching any dead ends). That is, there are no “gaps” in the walls of the structure. Closed-form structures can be made up of a plurality of chambers, a chamber being defined as a portion of the closed-form which by itself passes the closed-form trace test. Open-form structures are those structures where the walls of the structure in a plan view cannot be traced an infinite distance without reaching a dead-end or open-ended wall, no matter which way the trace progresses or where the trace is initiated. A combination-form structure has one or more chambers and one or more open-ended walls associated therewith (i.e., it is comprised of both a closed-form structure component and an open-form structure component). The present invention is useful for constructing relatively short concrete structures. By “relatively short” I mean the final height of the structure is not significantly proportionally larger than the width, length, breadth or diameter of the structure. Examples of relatively short closed-form and open-form reinforced concrete structures include thickener tanks, mixing tanks, ponds, shallow bins, bunkers, retaining wall enclosures, retaining walls, tunnel walls, columns, column bents, bearing walls, sound walls, and curtain walls. The present invention is also particularly useful for constructing relatively tall concrete structures. B y “relatively tall” I mean the final height of the structure is significantly proportionally larger than the width, length, breadth or diameter of the structure. Examples of relatively tall closed-form structures include silos, stacking tubes, towers, cooling towers, tower and tank stems, tanks, chimneys, and bins. Examples of relatively tall open-form and combination-form structures include corrugated retaining walls, silo-open storage bunkers, stacking walls, corrugated sound walls, arch dams, and high-rise shear walls.
Prior art methods of constructing relatively short concrete structures, such as shear walls, typically employ conventional forming techniques. For relatively short structures, such as straight walls, conventional reinforced plywood forms are frequently used. For forming relatively short curved walls, prior art construction methods include those described in U.S. Pat. No. 4,915,345 (Lehmann) and U.S. Pat. No. 5,125,617 (Miller et. al.). Prior art methods for constructing relatively tall closed-form concrete structures typically employ one of two approaches: (1) the jump-form method of construction, as generally described in U.S. Pat. No. 3,871,612 to Weaver; or (2) the slip form method of construction, such as generally described in U.S. Pat. No. 5,241,797. However, relatively tall open-form and combination-form structures are not addressed by slip-forming or jump-forming, and are not economical with conventional forming methods except as they are done in a “relatively short” format. This means that these types of relatively tall, open-form structures are not currently produced in a systematic or machine-like fashion, as are relatively tall closed-form structures.
Prior art methods of constructing vertical concrete structures also employ the method of segmental casting. Segmental casting or construction is generally defined as forming sections or segments of a larger reinforced concrete structure (e.g. a closed-form structure such as a silo, or an open-form structure such as a tall retaining wall) in vertical or near vertical segments which are cast with discrete horizontal or near-horizontal levels or cold joints (as in jump-forming) or in a continuous fashion (as in slip-forming). A complete structure is constructed by casting multiple, vertical or near-vertical segments either immediately adjacent to each other, or with gaps between them which are later filled with filler or closure segments which are cast in the same or similar manner. A structure cast in vertical segments can be identified as having vertical or near-vertical construction joints running the full height of the structure.
The distinction of “relatively tall” and “relatively short” structures is best defined by the construction methods typically employed to construct these structures, and the inherent technical and economic reasons for using such methods. Tall structures tend to be closed-form structures for storing bulk materials, and so that they will be of sufficient rigidity and strength to contain the stored materials and, even during construction, they will be of sufficient rigidity and strength against horizontal loadings such as wind and seismic forces. Tall, closed-form structures also tend to be prismatic, and are often symmetrical about the vertical axis. Accordingly, there are economic efficiencies to be gained in taking a less labor intensive, more system-like or machine-like approach to forming the closed-shape. As a result, the prior art method typically employed is jump-forming or slip-forming, which lend themselves more readily to discrete or continuous casting of tall structures. Short structures typically do not have the geometric efficiencies of tall structures and construction methods thereof typically employ conventional forming methods rather than more specialized methods such as jump-forming or slip-forming. In conventional forming methods the concrete forms are often close enough to the ground or floor level to allow for an entirely different means of external stability than is afforded when the forms are a great distance from the ground, and therefore allow for a less costly platform, work deck, or floor access to the work. A shear wall chamber in a building, for example, though it may be relatively tall compared to the building itself, is normally constructed between floors, using each floor as a work platform, and therefore it is not considered “relatively tall”. Such a wall would, however, be considered as “relatively tall” if it is free-standing for at least several floor heights or more during construction. In summary, relatively short structures are those which are typically produced using conventional forms because they are only a few stories tall and can therefore be economically accessed and manipulated from the ground or floor level, and relatively tall structures are those which are more than a few stories tall and require more of a machine-type approach to be most economically accessed and manipulated to accomplish the casting of reinforced concrete.
In the prior art jump-form method of construction, a cylindrical shell (closed-form) structure is produced using a series of inside and outside steel forms continuously attached together within either of the two concentric rings, but not between the rings. The rings are stacked one upon another and poured with concrete one level (levels typically vary 2′ to 6′ high) at a time until such time as they are 2 or more levels high. Then the bottom-most set of inside and outside forms are “jumped” or stacked on top of the top-most set of forms. This “jump” process is repeated until the structure height is achieved. Such an approach realizes a structure comprised of vertically-stacked, monolithic closed-form rings (typically 2′ to 6′ in height and 8″ to 2′ in thickness) with “cold” construction joints between rings. Important elements of the prior art jump-form method of construction are as follows: (1) The forces of the fluid concrete are resolved in the hoop rigidity of the circular ring of forms, and therefore the diameter of the structure is limited to a finite diameter, the fluid concrete forces of which are not greater than the tensile capacity of the forms and form fasteners; (2) the forms are moved upward separately of the work deck by mechanically “jumping” them with jib cranes to the next level, and the work deck moves upward with the use of climber winches which thrust off of the inside forms or off of supports which support from the ground and/or intermittently along the height of the inside surface of the structure; (3) plumbness of the structure is maintained by references with a transit or plumbob and repositioning of the form heights about the vertical axis of the structure in subsequent “jumps”; (4) the work deck is only on the inside of the concrete cylinder being constructed; (5) in order to raise the inside forms, the work decking must be removed or tilted out of the way frequently, or gaps must be left between the deck and the wall face; (6) the jump-form system must be thoroughly assembled and configured into a cylindrical shape from a large number of small, modular pieces; and (7) the forms are released from the concrete surface by prying them off manually, typically one-at-a-time.
In the slip-form method of construction, a closed-form shell structure is effected by moving a single level of concentric, typically plywood forms (commonly 4′ tall) continuously upward while installing rebar and pouring concrete until the structure height is achieved. Such an approach realizes a structure that is essentially monolithic throughout to the extent that the constructor keeps the operation continuous and there are no cold joints. Important particulars of the slip-form method of construction are the following: (1) unlike the jump-form method, the inside and outside forms are tied together with yokes (spaced approximately every 2′ to 8′, depending on the structure requirements for the form, around the entire perimeter of the structure section) and therefore the forces of the fluid concrete are resolved in the moment rigidity of the form-yoke combination; (2) the forms hold themselves and the accompanying work deck to the structure via a combination of pipes (which become buried in the concrete of the structure) and jacks that tie into the form-yoke system; (3) the forms and work deck(s) move upward together via thrust of the jacks on the pipes; (4) plumbness of the structure is maintained by references with a transit or plumbob and the form-deck system is re-oriented about the vertical axis of the structure by differential movement of the many jacks that support the forms and deck around the perimeter of the structures. There is an inherent flexibility of the pipes which, in conjunction with any imbalance of the deck load, often causes the deck and forms to “spin” or “sway”. This must be controlled by some means of bracing the pipes against the structure and/or rebar in the structure. There is currently no standard practice for controlling sway; (5) the main work deck is primarily on the inside of the shell or walls of the closed-form structure being constructed, with a swing scaffold hanging from the outside forms to allow finishing of the concrete surface; (6) the inside work deck spans across the diameter or span of the structure and is often comprised of the roof beams and roof decking; (7) the work deck is constructed such that there is little or no gaps between the deck and the forms; (8) the slip-form is typically not modular or re-usable and must be thoroughly constructed and configured into the closed-form shape from a large number of raw material pieces such as steel beams, lumber, and plywood; and (9) the forms are released from the concrete formed surface automatically and continuously since slip-forming is a continuous process.
In the conventional forming method for relatively “short” closed-form and open-form structures, a structure is produced by attaching the typically rectangular forms together into panels to form a partial or total wall or structure height. These panels are then backed by whalers to stiffen them between tie points, are tied through the wall by snap ties or through-bolts, and are usually braced or “kicked” to the ground or to a nearby floor level or structure with strut supports to plumb and stabilize the forms. Curvilinear structures are produced with either increments of straight forms or with special curvable forms. These specialized forms are a modified version of the straight form, with allowance for the form stiffeners and/or whaler system to be set manually to a certain radius. In either the straight wall or curved wall conventional form systems the work platform typically has no particular function other than as access to the work at the top of the forms. Important particulars of the conventional forming method of construction are as follows: (1) Unlike the jump-form method or the slip form method, the inside and outside forms are tied together with special ties that remain in the concrete, or through-bolts which are extracted after casting the concrete, and therefore the forces of the fluid concrete are resolved in the tensile rigidity of the tie or through-bolt; (2) the forms and work plafform(s) are moved upward manually and separately after removal of the ties or through-bolts, and typically a level of forms is left at the top of a pour to rest the next set of forms upon; (3) plumbness of the structure is maintained by references with a level, transit or plumbob, and the form-plafform system is re-oriented about the vertical axis of the structure by adjusting the kicker struts; (4) the work deck is attached to the forms and therefore spans along the perimeter (as compared to jump-forms and slip-forms which span across the formed opening); (5) the work platform being attached to the forms has a small gap between them and the form; (6) the conventional form system must be thoroughly assembled and configured from a large number of small, modular pieces to form a structure; and (7) the forms a re typically released manually from the formed surface by prying action.
There are several shortcomings with the prior art. Specifically: (1) Vertical segmental construction is not addressed by jump-form or slip-form methods of construction; (2) although segmental construction is addressed by conventional means, only relatively short structures can be economically effected by conventional means (i.e., conventional forming methods of construction are not economically adaptable for construction of tall, closed-form or open-form structures); (3) although accurate geometric measurement is possible with all methods of construction given modern surveying equipment, accurate geometric control is not inherently achievable for relatively tall and/or large footprint structures constructed with the current jump-form or slip-form methods of construction; (4) modern jump-forming and slip-forming techniques are very labor intensive; (5) none of the three concrete forming methods described above (jump-forming, slip-forming, and conventional forming) are readily adaptable to both discrete and continuous forming; (6) the methods by which jump-forms, slip-forms, and conventional forms are borne by the evolving structure is cumbersome to productivity; (7) in all three forming methods there are significant limitations on geometries due to the method of resolution of the hydrostatic force of the concrete between the inside and outside forms; and (8) jump-forming inherently does not allow for a work deck on the outer ring of forms.
The reason why conventional forms are not readily adaptable for construction of tall, open-form structures is inherent in the method: the process of loosening the forms from the wall-ties or through-bolts, lifting the forms vertically to the next level, and attaching the wall-ties or installing the through-bolts is a very cumbersome, labor intensive operation. It also requires the continuous use of very large cranes for great heights.
None of the prior art methods of constructing concrete structures address both discrete and continuous modes of operation in the vertical or near vertical direction. Jump-forms are not designed, nor are they readily adaptable for, slip (continuous) forming. Slip-forms are not designed, nor are they readily adaptable for, discrete forming. Although discrete forming with slip-forms may be an inadvertent result of stopping the slip form operation and letting the concrete set-up, it is not an intended function, nor is it a simple matter to get a slip-form moving again when the concrete sticks solidly to the forms. Conventional form systems are either designed to be used for horizontal slip-forming (e.g. a tunnel slip-form) or are designed for static (discrete) casting. They cannot be readily transitioned for use in a bi-model fashion.
Slip forms, though relatively failsafe in the sense that the support pipes are continuously buried in the wall, are inherently cumbersome for placing rebar and concrete because the pipe and yoke system repeats itself so frequently around the perimeter. Because of this, structures with dense rebar and/or large perimeters are impractical with slip-forming. The through-bolt or tie system which holds conventional forms to the concrete structure also support the work platforms. This “tie-through” method of resolving the hydrostatic forces from the concrete and attaching the forms to the concrete is cumbersome to upward progression because of the labor-intensive process of removing and re-inserting bolts or ties. In the prior art chord-form method of construction a vertical portion or vertical segment of a cylindrical structure is formed by tensioning the concentric set of jump-forms (of the type described in U.S. Pat. No. 3,871,612, being approximately 4′ tall by 6′ long) to buttress trusses which are positioned vertically at either end of the vertical segment in modular lengths that are a multiple of the form height. A chord deck and an outside wrap-a-round deck span between these buttress trusses, allowing access to both sides of the segment of jump forms. As with jump-forming, jib cranes are used to raise or “jump” the forms and climber winches are used to raise the chord deck that interfaces with the perimeter of the evolving wall segment. As a supplementary hoisting method to the climber winches, the inside and outside chord trusses and attached work-deck are hoisted by way of hydraulic cylinders along guides on the buttress trusses. Closure segments are effected by reconfiguring parts of the buttress trusses and bolting them to the adjacent segments.
There are a number of shortcomings with the prior-art chord-form method: (1) As with the classical jump-form method which relies on the hoop tensile capacity of the forms to resolve the hydrostatic forces from the concrete, there is a practical limitation on both the geometry and maximum diameter which can be achieved. The geometry is limited to curved walls, and the radius of the curved wall is limited to that finite value where the fluid concrete forces are not greater than the tensile capacity of the forms and form fasteners. A 60′ radius curve is the practical limit for using these types of forms; (2) As with jump-forming, the chord-form method requires two or more levels of forms, and it requires that these forms be “jumped”, a very labor intensive process; (3) The chord-form method requires heavy buttress trusses at both ends for the full height of the segment being constructed. The capital and mobilization costs associated with these trusses are very high and set-up times are long, especially for very tall segments; (4) Vertical alignment of the segment can only be achieved when each new buttress truss is installed, and only to the degree to which the truss can be tilted out of plumb to correct the alignment.
What is needed then is a method of, and apparatus for, constructing vertical or near-vertical concrete structures which achieves the benefits to be derived from similar prior art methods and devices, but which avoids the shortcomings and detriments individually associated therewith.